Spacer design for mitigating stray light

ABSTRACT

Spacers for separating a first lens element from a second lens element, lens modules including such spacers and digital cameras including such lens modules. A spacer may comprising along its perimeter at least one contact section being in contact with the first lens element and the second lens element and at least one non-contact section being separated from the first lens element. The at least one non-contact section comprises an internal inclined surface having designed to reduce or mitigate stray light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.16/975,718 filed Aug. 26, 2020 (now allowed), which was a 371application from international patent application PCT/IB2019/051643filed Mar. 1, 2019, which claims priority from U.S. Provisional PatentApplication No. 62/637,451 filed Mar. 2, 2018, which is expresslyincorporated herein by reference in its entirety.

FIELD

The presently disclosed subject matter is related in general to lensesof digital cameras, including folded digital cameras.

BACKGROUND

A typical digital camera includes an image sensor (or simply “sensor”)and a lens (also known as “lens assembly”, or “lens module”). The lensforms an image on the sensor. A lens may include several lens elements,typically assembled in one lens barrel. Folded cameras (FCs) anddouble-folded cameras (DFCs) are known, see for example co-owned U.S.Pat. No. 9,392,188, which is incorporated herein by reference in itsentirety.

SUMMARY

According to some examples of the presently disclosed subject matter,there are provided spacers for separating a first lens element from asecond lens element, a spacer comprising a spacer perimeter including acontact section being in contact with the first lens element and thesecond lens element and a non-contact section being separated from thefirst lens element.

In addition to the above features, the spacer according to this aspectof the presently disclosed subject matter can optionally comprise one ormore of features (i) to (viii) below, in any technically possiblecombination or permutation:

-   -   i. wherein the non-contact section comprises a non-contact        section internal inclined surface having a height D2 extending        between an internal contour of the spacer to a base of the        non-contact section internal inclined surface, wherein the        spacer perimeter has a thickness t extending between a contact        point of a back face of the spacer facing the second lens        element and a contact point of a front face of the spacer facing        the first lens element, and wherein an inclination of the        non-contact section internal inclined surface is greater than a        ratio D2/t,    -   ii. wherein height D2 is perpendicular to thickness t,    -   iii. wherein the contact section comprises a contact section        internal inclined surface having an inclination less steep than        the inclination of the non-contact section internal inclined        surface,    -   iv. wherein the first lens element is at an object side relative        to the spacer and wherein the second lens element is at an image        side relative to the spacer,    -   v. wherein an optical part of the first lens element or the        second lens element is non-circular,    -   vi. wherein the spacer is included in a camera comprising an        image sensor, wherein the non-contact section internal inclined        surface is designed to redirect stray light so it does not hit        the image sensor,    -   vii. wherein the sensor is characterized by at least two sides,        and wherein each side is characterized by a different length,    -   viii. wherein the sensor is characterized by a non-circular        shape.

According to some examples of the presently disclosed subject matter,there are provided lens modules comprising a plurality of lens elementsordered along a lens symmetry axis from an object side to an image side,each lens module comprising a spacer situated between a lens element anda consecutive lens element from among the plurality of lens elements,the spacer comprising along its perimeter a contact section being incontact with the first lens element and the second lens element and anon-contact section being separated from the first lens element. Aspacer in such a lens module may comprise one or more of features (i) to(viii) above, in any technically possible combination or permutation.

According to some examples of the presently disclosed subject matter,there are provided digital cameras, each digital camera comprising alens module accommodating a plurality of lens elements ordered along alens symmetry axis from an object side to an image side and at least onespacer situated between a lens element and a consecutive lens elementfrom among the plurality of lens elements, the spacer comprising aspacer perimeter including a contact section being in contact with thefirst lens element and the second lens element and a non-contact sectionbeing separated from the first lens element. A spacer in such a digitalcamera may comprise one or more of features (i) to (viii) above, in anytechnically possible combination or permutation.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples are described below with reference to figuresattached hereto that are listed following this paragraph. Identicalstructures, elements or parts that appear in more than one figure aregenerally labeled with a same numeral in all the figures in which theyappear. The drawings and descriptions are meant to illuminate andclarify examples of the subject matter disclosed herein, and should notbe considered limiting in any way. In the drawings:

FIG. 1A shows schematically a lens in a general isometric view;

FIG. 1B shows a cut through a lens barrel carrying the lens of FIG. 1A,together with a stray light ray path through the barrel to an imagesensor, according to examples of the presently disclosed subject matter;and

FIG. 1C shows first and second object side lens elements of the lens ofFIG. 1A, separated by a spacer;

FIG. 1D shows in (a) a front, object side, and in (b) a back, image sideof the spacer of FIG. 1B;

FIG. 2A shows schematically a lens in a general isometric view,according to examples of the presently disclosed subject matter;

FIG. 2B shows a cut through a lens barrel carrying the lens of FIG. 2A,together with a stray light ray path through the barrel to an imagesensor, according to examples of the presently disclosed subject matter

FIG. 2C shows first and second object side lens elements of the lens ofFIG. 2A, separated by a spacer, according to examples of the presentlydisclosed subject matter; and

FIG. 2D shows in (a) a front, object side and in (b) a back, image sideof the spacer of FIG. 2B, according to examples of the presentlydisclosed subject matter.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding. However, it will beunderstood by those skilled in the art that the presently disclosedsubject matter may be practiced without these specific details. In otherinstances, well-known methods have not been described in detail so asnot to obscure the presently disclosed subject matter.

It is appreciated that certain features of the presently disclosedsubject matter, which are, for clarity, described in the context ofseparate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features of the presently disclosedsubject matter, which are, for brevity, described in the context of asingle embodiment, may also be provided separately or in any suitablesub-combination.

It is appreciated that unless explicitly set forth otherwise, terms suchas “first”, “second”, “third” and so forth as used herein, are notnecessarily meant to imply a particular order, but are only meant todistinguish between different elements or actions. For example, a firstlens element and second lens element as used herein do not necessarilyrefer to the pair of lens elements in lens 100 disclosed herein below,which are located closest to the object side, and may refer to adifferent pair of lens elements located elsewhere in lens 100, e.g.second and third lens elements.

Stray light is an undesirable effect where light in an optical system.Stray light is light not intended to enter the optical system accordingto an optical design, but nonetheless reaches the sensor. In some cases,stray light may come from an intended source (e.g. light reflected froman object in the field of view of the camera), but follows paths otherthan the intended path (optical path that does not pass through theoptical area of all lens elements in a lens module on its path to thesensor). In other cases, stray light may come from a source other thanthe intended source (e.g. outside the camera field of view (FOV)).

For example, FIG. 1B shows schematically a camera 150 comprising a lens(numbered 100 in FIG. 1A) with stray light 220 reflected from aninternal spacer R1 onto an image sensor 104 (as described in more detailbelow). FIG. 1A shows lens 100 in a general isometric view. Lens 100includes a plurality (N) lens elements L, (wherein “i” is an integerbetween 1 and N) shown in a decomposed view where the different lenselements are illustrated separately. L₁ is the lens element closest tothe object side and L_(N) is the lens element closest to the image side,i.e. the side where the image sensor is located. In lens 100 N=5. Thisis however not limiting, and a different number of lens elements can beused. According to some examples, N is equal to or greater than 3. Forexample, N can be equal to 3, 4, 5, 6 or 7. The coordinates X-Y-Z applyin all other respective views where not marked. The lens elements aresituated along an optical axis 108 that is aligned with the Z axis fromobject side to the sensor at the image side.

Each lens element L_(i) comprises a respective front surface S_(2i-1)(the index “2i−1” being the number of the front surface) and arespective rear surface S_(2i) (the index “2i” being the number of therear surface), where “i” is an integer between 1 and N. This numberingconvention is used throughout the description. Alternatively, asindicated throughout this description, lens surfaces are marked as“S_(k)”, with k running from 1 to 2N. The front surface and the rearsurface can, in some cases, be aspherical. This is however not limiting.As shown in FIG. 1A, in some examples, an optical part (i.e. partutilized for light passage toward the sensor) of the first lens elementL1 is non-circular, e.g. it has flat top and bottom sections.

FIG. 1B illustrates a side view of a cross section of camera 150. Camera150 comprises lens barrel 102, wherein the lens elements Li and spacersRi of lens 100 are situated within lens barrel 102. Camera 150 furthercomprises image sensor 104 and an optional optical element (e.g. aninfrared filter) 106. In the example shown, two adjacent lens elementsare separated by a spacer marked “R₁”. Thus, lens elements L1 and L2 areseparated by a spacer R1, lens elements L2 and

L3 are separated by a spacer R2, lens elements L3 and L4 are separatedby a spacer R3, and lens elements L4 and L5 are separated by a spacerR4.

As used herein the term “front surface” of each lens element or spacerrefers to the surface of a lens element or spacer located closer to theentrance of the camera (camera object side) and the term “rear surface”refers to the surface of a lens element or spacer located closer to theimage sensor (camera image side).

An enlarged view of lens elements L1 and L2 separated by spacer R1 isshown in FIG. 1C, and front (object side) and back (image side) views ofspacer R1 are shown in FIG. 2D. Each spacer is designed to have aperimeter and an opening at its center for allowing light passagetherethrough towards the sensor. The perimeter can be in contact with afirst lens element at one side and a second lens element at the otherside. The use of spacers in a lens assembly is known in the art.

An example of a lens design that may exhibit stray light is describedwith reference to FIGS. 1B and 2B. In the illustrated example, straylight 120 in camera 150 may arrive for example from reflection oninternal surfaces of spacer R1 (facing an internal opening 118) and thusdepends on the shape of spacer R1 (and in particular the shape of itsinternal surfaces). In the example shown, when assembled in the barrel,a back surface S2 of lens element L1 touches spacer R1 over entire frontcontact surface 110 of spacer R1, including at bottom and top frontsurface contact sections 110 a and 110 b. A front surface S3 of lenselement L2 touches spacer R1 over an entire back contact surface 112 ofspacer R1, including at bottom and top back surface contact sections 112a and 112 b. The distance between contact points of front contactsurface 110 a and back contact surface 112 a, along the Z axisdirection, defines a spacer thickness t, which for spacer R1 is markedas t1.

An internal surface 114 of spacer R1 between an edge 114 a of a frontcontact section 110 a and an edge 114 b of a back contact section 112 ahas a length D3 and an inclination (angle) a. Spacer R1 has a height D2(also shown in FIG. 1B) of back contact section 112 a (substantiallyperpendicular to thickness t1) extending between an internal contour ofthe spacer (an edge of the internal opening 118 as indicated by arrow115 a in FIG. 1D) and a base 115 of the inclined surface (indicated byarrow 115 b), setting the inclination (angle) a. In some cases, spacerR1 may also have a thickness D1 of front bottom contact section 110 a,extending from the base 115 of the spacer in the X direction towards anexternal edge of the spacer (indicated by arrow 115 c). Notably asimilar surface 114 and thicknesses D1 and height D2 exist at the top ofspacer R1 (i.e. the lens is axi-symmetric radially along axis X). Inother examples, other or additional inclination surfaces similar to 114may exist at other locations around the perimeter of the spacer. Asmentioned above, inclination α is determined by spacer thickness t1 andheight D2, where tan α=D2/t1.

According to the illustrated example, given the design of the first lenselement L1 and angle α and as shown in FIG. 1B, a stray light ray 120entering the lens from the object side is refracted by lens element L1,hits surface 114 of spacer R1, reflected from the surface, and continuesthrough the lens along an optical path terminating at the image sensor104 at a point 122.

According to the subject matter disclosed herein, it is suggested tosolve the problem of stray light described above by a specialspacer-design devised for this purpose. Examples of the spacer designare described with reference to FIGS. 2A-2D. FIG. 2A shows schematicallya lens numbered 200 according to an example of the presently disclosedsubject matter in a general isometric view. Lens 200 is shown in adecomposed view where the different lens elements are illustratedseparately. FIG. 2B shows first and second object side lens elements oflens 200, separated by a spacer R1′. FIG. 2C illustrates a side view ofa cross section of a camera 250. Lens 250 comprises lens barrel 202 thataccommodates lens 200. Camera 250 further comprises image sensor 104 andoptional optical element 106 (e.g. IR filter). FIG. 2C furtherillustrates a stray light ray 220 passing through the barrel in theobject side direction. FIG. 2D shows in (a) a front, object side and in(b) a back, image side of the spacer of FIG. 2B.

By way of example lens 200 is shown to include five lenses, similar tolens 100. As mentioned above, this example is not meant to be limitingand a different/greater number of elements is likewise contemplated.According to an example, all the elements of lens 200 are similar tothose of lens 100, except for an “improved” first spacer numbered R1′located between lens elements L1 and L2. Spacer R1′ has a more steeplyinclined internal surface (positive slope) 214, having an inclinationangle α′ greater than α, for example an angle α′=33.3°, as compared toangle α that equals about 20°. The steeper inclination is achieved insome examples, by shortening the length between edges 214 a and 214 b(as compared to 114 a and 114 b above) to obtain length of inclinationD3′. In some examples the height D2 is the same as that of spacer R1.Notably, increasing the inclination angle by increasing height D2 mayhave an adverse effect, as it would reduce the open space at the center(opening 118) of the spacer, causing increased blockage of light passingthrough the lens.

Different than lens 100 described above, where contact between S2 and R1occurs over the entire front contact surface 110, here the shorterlength of D3′ (relative to D3) results in no-contact sections in R1′(e.g. at the bottom and top), which are separated from surface S2 oflens L1 (i.e. section illustrated as contact sections 110 a and 110 b inspacer R1). Contact sections 210 a and 210 b, which are in contact withS2, are located adjacent to the no-contact sections. By allowing nocontact between the spacer R1′ and S2 at certain sections of the spacer,it is made possible to increase the inclination angle. According to thesuggested design, the inclination of the internal inclined surface isgreater than a ratio between height D2 and thickness t1, such that, tanα>D2/t1. As a result of the steeper inclination of the internal bottomsurface 214, stray light ray 220 entering the lens from the object sideis refracted by lens element L1, hits surface 214 of spacer R1′ andcontinues through the lens along an optical path that misses imagesensor 104.

The changes in lens 200 and specifically in spacer R1′ as describedabove introduce significant design flexibility. The increasedinclination of a surface such as surface 214 reduces stray light.

The example of surface 214 as a bottom and/or top surface of R1′ is notlimiting in any way: one, two or more such surfaces can be formed aroundthe circumference of spacer R1′ e.g. facing surface S2. In an embodiment(not shown), surface S2 may contact spacer R1′ at only three points onits front contact surface, such that most of the side edges includeno-contact surfaces (with steeper inclination) such as surface 214.

It is noted that while the description above refers to a non-circularlens element (having flat top and/or bottom sections), this should notbe construed as limiting. According to other examples, the lens elementmay be circular, with a lens and/or camera including such a circularlens element still benefiting from reduction in stray light due to aspacer design as disclosed herein. The presently disclosed subjectmatter can be used for mitigating the stray light problem, where theproblem exists in one or more sections of the perimeter of the spacer.

As explained above, stray light entering the lens from the object sideis refracted by lens element L1, hits some part of the surface of thespacer, and continues through the lens along an optical path towards thesensor. Considering for example a sensor characterized by a rectangularshape, due to the difference in shape between the sensor and the lens(having a circular or substantially circular shape), stray light may hitthe sensor when reflected from one side of the spacer, and may miss thesensor when reflected from another side of the spacer. Such differencesmay also be encountered when the sensor is characterized by sides havingdifferent lengths, such as in the case of a rectangular sensor, which isnot square shaped.

A spacer (e.g. R1′ located between lens elements L1 and L2) can beadapted as described above to have a more steeply inclined internalsurface 214 at the sides of the spacer that reflect the stray light soit does not hit the sensor. The higher inclination can be achieved byshortening the length between edges 214 a and 214 b and obtaining anon-contact section D3′, as mentioned above.

It is noted that a digital camera (150, 250) discussed hereinabove maybe a multi-aperture camera that includes one or more additional uprightcameras as well as one or more folded cameras. A folded camera comprisesa reflecting element (e.g. a mirror or prism) configured to fold lightincoming along a first optical path from an object side to a secondoptical path (substantially perpendicular to the first optical path)along the lens symmetry axis towards the sensor. An example of a foldedcamera is described in U.S. Pat. No. 9,392,188, which is incorporatedherein by reference in its entirety.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.The disclosure is to be understood as not limited by the specificembodiments described herein, but only by the scope of the appendedclaims.

Unless otherwise stated, the use of the expression “and/or” between thelast two members of a list of options for selection indicates that aselection of one or more of the listed options is appropriate and may bemade.

All references mentioned in this specification are herein incorporatedin their entirety by reference into the specification, to the sameextent as if each individual reference was specifically and individuallyindicated to be incorporated herein by reference. In addition, citationor identification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the present application.

What is claimed is:
 1. A spacer for separating a non-circular first lenselement from a second lens element, the spacer comprising: a spacerperimeter including a contact section being in contact with the firstlens element and the second lens element and a non-contact section beingseparated from the first lens element, wherein the non-contact sectioncomprises a non-contact section internal inclined surface having aheight D2 extending between an internal contour of the spacer to a baseof the non-contact section internal inclined surface, wherein the spacerperimeter has a thickness t extending between a contact point of a backface of the spacer facing the second lens element and a contact point ofa front face of the spacer facing the first lens element, and wherein aninclination of the non-contact section internal inclined surface isgreater than a ratio D2/t.
 2. The spacer of claim 1, wherein height D2is perpendicular to the thickness t.
 3. The spacer of claim 2, whereinthe contact section comprises a contact section internal inclinedsurface having an inclination less steep than the inclination of thenon-contact section internal inclined surface.
 4. The spacer of claim 1,wherein the first lens element is at an object side relative to thespacer and wherein the second lens element is at an image side relativeto the spacer.
 5. The spacer of claim 1, wherein an optical part of thefirst lens element or the second lens element is non-circular.
 6. Thespacer of claim 1, included in a camera comprising an image sensor,wherein the non-contact section internal inclined surface is designed toredirect stray light so it does not hit the image sensor.
 7. The spacerof claim 6, wherein the sensor is characterized by having at least twosides, and wherein each side is characterized by a different length. 8.The spacer of claim 6, wherein the sensor is characterized by having anon-circular shape.
 9. A lens module comprising: a plurality of lenselements ordered along a lens symmetry axis from an object side to animage side; and a spacer situated between a lens element and aconsecutive lens element from among the plurality of lens elements, thespacer comprising along its perimeter a contact section being in contactwith the first lens element and the second lens element and anon-contact section being separated from the first lens element.
 10. Thelens module of claim 9, wherein the non-contact section comprises anon-contact section internal inclined surface having a height D2extending between an internal contour of the spacer to a base of thenon-contact section internal inclined surface, wherein the spacerperimeter has a thickness t extending between a contact point of a backface of the spacer facing the second lens element and a contact point ofa front face of the spacer facing the first lens element, and wherein aninclination of the non-contact section internal inclined surface isgreater than a ratio D2/t.
 11. The lens module of claim 10, wherein theheight is perpendicular to the thickness.
 12. The lens module of claim9, wherein the contact section comprises a contact section internalinclined surface having an inclination less steep than the inclinationof the non-contact section internal inclined surface.
 13. The lensmodule of claim 9, wherein the first lens element is at an object siderelative to the spacer and wherein the second lens element is at animage side relative to the spacer.
 14. The lens module of claim 9,wherein an optical part of the lens element or the consecutive lenselement is non-circular.
 15. The lens module of claim 9, included in acamera comprising an image sensor, wherein the non-contact sectioninternal inclined surface is designed to redirect stray light so it doesnot hit the image sensor.
 16. The lens module of claim 15, wherein theimage sensor is characterized by having at least two sides and whereineach side is characterized by a different length.
 17. The lens module ofclaim 15, wherein the image senor is characterized by having anon-circular shape.
 18. A digital camera comprising: a lens moduleaccommodating a plurality of lens elements ordered along a lens symmetryaxis from an object side to an image side and at least one spacersituated between a lens element and a consecutive lens element fromamong the plurality of lens elements, the spacer comprising a spacerperimeter including a contact section being in contact with the firstlens element and the second lens element and a non-contact section beingseparated from the first lens element.
 19. The digital camera of claim18, wherein the non-contact section comprises a non-contact sectioninternal inclined surface having a height D2 extending between aninternal contour of the spacer to a base of the non-contact sectioninternal inclined surface, wherein the spacer perimeter has a thicknesst extending between a contact point of a back face of the spacer facingthe second lens element and a contact point of a front face of thespacer facing the first lens element, and wherein an inclination of thenon-contact section internal inclined surface is greater than a ratioD2/t.
 20. The digital camera of claim 18, wherein the digital camera isa folded camera, further comprising and image sensor and a reflectingelement configured to fold light incoming along a first optical pathfrom an object side to a second optical path along the lens symmetryaxis towards the image sensor.